The results presented in Chapter 6 and Chapter 7 so far have considered TV video traffic downloaded from the video head-end to network nodes, but have not included regular traffic. However, some IPTV service providers cater for both video and non-video services including web, email, data, gaming and interactive TV. In this section, some of the previous scenarios are re-evaluated assuming that the network traffic comprises both regular and TV video traffic.
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7.7.1 Traffic Mixtures
In addition to the formerly evaluated network traffic having only TV video traffic, four further traffic mixtures are considered:
1. 10 – 90: Internet traffic reports forecast that by 2016 Internet video traffic will account for about 80%-90% of total Internet traffic [2].
2. 30 – 70: This is based on the fact that the 80%-90% share of video in the total traffic is made up of various types of video including TV along with VoD and to-Peer. Consequently, this mixture considers the situation where regular, VoD and Peer-to-Peer traffic represent 30% of the traffic and the remaining 70% of network traffic is TV video.
3. 50 – 50: This traffic mixture represents a service having equal amounts of regular and TV traffic.
4. 70 – 30: The traffic mixture considered here is that of a service provider whose main service is not TV but still carries some TV video content having 70% regular traffic and 30% TV traffic.
7.7.2 Power Consumption Evaluation
The intention is to investigate how the presence of regular traffic along with TV traffic influences the power consumption. The evaluation considers three network schemes that were evaluated in the previous sections: deploying caches of fixed sizes at the network nodes, performing time-based content replacements on the contents of caches of fixed sizes and replacing the contents of variable caches. The fixed-cache
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MILP model proposed in Chapter 4 and content replacements MILP models are run after including regular traffic matrices in the input data.
Figure 7-10: Average network traffic demand considering TV video traffic and regular traffic where regular traffic is: 10%, 30%, 50% and 70% of the total (regular +
TV video) traffic
Under each considered traffic mixture, the total daily regular traffic is obtained from the total TV traffic using the traffic ratios that apply to each case. The regular traffic between each node pair is then generated using a random function with mean values compliant with the considered traffic mixtures. The trend and volume of regular traffic under each considered case are shown in Figure 7-10. The curves in Figure 7-10 show TV video and regular traffic components. Therefore the total traffic mixture of 10 – 90 for example can be calculated by adding the TV video traffic curve to the 10% regular traffic curve. The traffic volume is calculated from the average daily TV viewing
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figures in Figure 6-1 in Chapter 6 assuming that all TV programmes are delivered using HDTV. Therefore a peak traffic of over 260Tb/s can be observed which is moderate compared to future busy-hour Internet traffic that is expected to reach 720Tb/s in 2016 [108].
Table 7-1: Network maximum and average power savings (%) with different traffic mixtures under HDTV NSF-SVMP
Table 7-2: Network maximum and average power savings (%) with different traffic mixtures under HDTV BT 21CN-SV4
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Table 7-1 and Table 7-2 show the maximum and average savings in power consumption considering TV traffic only and the four assumed traffic mixtures when deploying caches of fixed sizes and when performing content replacements on caches of fixed and variable sizes under NSF-SVMP and BT 21CN-SV4, respectively. Deploying caches in the network reduces the traffic by storing popular TV programmes locally.
The presence of caches however does not reduce regular traffic passing through the network since the objects related to this traffic type are not stored in caches. Since the MILP models are linear, savings in power consumption are likely to be proportional to the portion of TV traffic in the traffic mixture. As can be inferred from Table 7-1 and Table 7-2, overall power savings are relative to the TV video component in the network traffic since maximum savings are attained when the traffic is made up of only TV and less power savings are achieved as the percentage of regular traffic increases in the traffic mixture. The linear property of the MILP models allows an estimated calculation of network power savings for any traffic mixture as long as the portion of traffic that will benefit from deployed caches is known.
Figure 7-11 and Figure 7-12 show the percentage of power savings over the time of the day when deploying caches of fixed sizes and when performing 12 content replacements on caches of fixed and variable sizes in the BT 21CN-SV4 topology.
Figure 7-11 shows the power savings with traffic mixtures 10 – 90 and 30 – 70 while Figure 7-12 considers the traffic mixtures 50 – 50 and 70 – 30. The peaks of regular traffic and TV traffic are not aligned (see Figure 7-10), resulting in a different trend of power consumption over the time of the day under each considered traffic mixture. If caches of fixed sizes are deployed in the network, moderate and comparable power
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savings are achieved over the time of the day. These savings become more diverse as the amount of regular traffic increases in the traffic mixture.
When 12 content replacements are performed on the contents of fixed caches, the amount of power savings vary over the time of the day since popularities of TV programmes are different over the time of the day resulting in different cache hit ratios. Nevertheless, the resultant average daily power savings are similar to those assuming fixed caches with no content replacements. The maximum power savings are attained under 12 content replacements with variable caches under all traffic mixtures. The combined influence of varying the size of the cache with respect to traffic and maximising cache hit ratios due to content replacements results in the greatest power savings compared to other methods.
Figure 7-11: Power savings (%) over the time of the day with fixed caching and when 12 content replacements are performed on fixed and variable size caches
under BT 21CN-SV4 with traffic mixtures of TV video only, 10 – 90 and 30 – 70
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Figure 7-12: Power savings (%) over the time of the day with fixed caching and when 12 content replacements are performed on fixed and variable size caches
under BT 21CN-SV4 with traffic mixtures of TV video only, 50 - 50 and 70 – 30